The present invention is specifically directed to an improvement in methods and apparatus for measuring radiant energy scattering characteristics of a test panel. Radiant energy scattering characteristics include transmittance and reflectance characteristics.
In the prior art, the following apparatus is used to measure transmittance and reflectance characteristics of a planar sheet of dielectric material at microwave frequencies. A test panel of the dielectric material is positioned in an anechoic chamber with two microwave antennas.
To measure the transmittance characteristics of the test panel over a circular arc the two antennas are positioned so as to be directed toward each other along a common same axis of propagation, and the test panel is positioned between the two antennas along the common axis. The radiation between the antennas is measured with the test panel absent, and is also measured with the test panel present to determine the percentage of incident radiation that is transmitted through the test panel.
The plane of the test panel is supported along a second axis that is normal to the common axis of propagation of the antennas and is selectively rotated about the second axis to enable the transmittance characteristics of the panel to be measured at a plurality of predetermined incidence angles.
To measure the reflectance characteristics of the panel both antennas are positioned on the same side of the test panel and are directed at the test panel with their respective axes of propagation at predetermined equal and opposite incidence angles. For each of a plurality of different predetermined incidence angles at which measurements are taken both antennas are repositioned and redirected. This method and apparatus for measuring the reflectance characteristics is obviously quite cumbersome.